This invention pertains to precision additive color photographic printing.
While a major portion of color photographs are now printed by the subtractive color system, the difficulty of exercising adequate control over the color rendition in the print is well known. In practice the exercise of human judgement and experience are required to produce acceptable prints.
The prior art has concerned itself with some sort of control that identifies or rejects color negatives that are poorly exposed and so would not allow satisfactory prints to be produced regardless of color correction, and to provide a satisfactory color balance in spite of "large area transmission densities" (LATD). In the latter case the abnormally large contribution of a wide expanse of colored blue sky, or of any other primary color, is minimized so that otherwise required color balance information is made available for the printing of the negative. This phenomenon has also been termed "subject failure."
One proposal of the prior art arranges for a visual inspection by the operator to discern "subject failure" negatives, and for a manual set of adjustments by the operator to minimize the defect. Certain automatic features are provided, such as centering a negative for printing in the printing gate from amongst the several negatives on a roll of negatives, and recording the color component printer information on magnetic tape.
Another proposal for subtractive printing senses insofar as possible the characteristics of the negative and makes normal or supernormal corrections. Capacitors are charged accordingly and the charge on each determines how long an exposure with which subtractive filter shall take place.
Another proposal for examining color transparencies (slides) by an additive color source employs a color cathode-ray tube. The particular transparency is placed upon the face of the tube, upon which an essentially white raster of light is created by a three-gun type embodiment. The electron beam current for each of the guns, red, green and blue, is adjusted until a pleasing rendition of the color subject matter of the transparency is obtained, as determined by the operator. The voltage upon the grid of each gun at this adjustment is a measure of the intensity of each of the primary colors that are then giving an "off-white" raster. This is recorded as the color information for further processing of the transparency. The system is employed particularly for obtaining color separation information for printing a color picture upon paper with color inks.
Another proposal employs an apparatus for measuring the exposure parameters of a negative, a computer for accepting that information, and a plurality of photographic printers for making plural prints from the negative in accordance with the computer information. This system is for black and white photography only.